Sydney's Olympic velodrome faces the end

How will Australia's role against IS work?

RAAF Hornets are expect to join the air campaign against Islamic State in Syria. Fairfax's Mark Kenny explains the government processes.

Defence Minister Marise Payne confirmed on Wednesday that Australia had rejected the request and would maintain its current contribution.

"Australia has considered the request from US Secretary of Defense Ash Carter in light of the substantial contributions we are already making to train Iraqi security forces and to the air campaign," a spokesman for the Minister said.

"The government has advised Secretary Carter that our existing contributions will continue."

In lieu of further military commitment, Australia would make an "important contribution to command roles" through an increase in the number of ADF personnel in coalition headquarters from 20 to 30, the spokesman said.

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US Ambassador to Australia John Berry played down the response, saying it elicited "absolutely no disappointment".

"There is great gratitude from Washington for the role Australia has played," he told the Seven Network.